Recommends Operators Of Type Cycle Throttles In Flight

British investigators are reasonably certain ice crystals blocked fuel lines on a British Airways airliner that landed short of the runway at London's Heathrow Airport in January.

As ANN reported, the Boeing 777-200ER was on an extended final to land at Heathrow on January 17, when the plane's autopilot commanded the 777's engines to spool up. Both engines responded initially... but thrust then dialed back to just above flight idle -- first in the right turbofan, then the plane's left engine. 

The plane's flight crew was later heralded for bringing the plane down safely, landing short of the threshold to Runway 27L at Heathrow. Only relatively minor injuries were reported to some of the plane's 136 passengers and 16 crew.

Investigators quickly ruled out a systems failure on the 777, or in its Rolls-Royce Trent 800 turbofans... and the airliner had plenty of fuel left after what had been an uneventful flight from Beijing, China. Officials then narrowed their search, looking for kind of problem with the plane's fuel.

The Air Accidents Investigation Branch determined the plane flew through unusually cold air over Siberia... and investigated the possibility the plane's fuel could have been affected. On Thursday, the AAIB said they've ruled that out... adding they now believe a larger-than-normal amount of water contained in the fuel froze, and the resulting ice crystals blocked the fuel lines as they melted while the 777 descended to land.

Officials theorize the amount of water was enough to overwhelm the Fuel Oil Heat Exchangers on both engines, which are designed to melt ice crystals and vaporize the water. The AAIB also recommended all 777 operators periodically increase engine thrust levels while operating in the flight levels... a time when engine power is usually reduced to low-levels, which may allow excessive ice to form.

The National Transportation Safety Board heralded the AAIB's report Thursday, stating the investigation was assisted by a US team that included NTSB specialists, the Federal Aviation Administration, and Boeing.

"When it comes to aviation safety, there are shared interests that transcend national borders," said NTSB Chairman Mark Rosenker, adding the Board has issued a recommendation to the FAA and EASA to consider the implications the AAIB's findings may have on the 777, and other airliners.

FMI: Read The AAIB Interim Report (.pdf), www.ntsb.gov